Vasorelaxing effects of Caesalpinia sappan -: Involvement of endogenous nitric oxide

Methanolic extract and two purified compounds (brazilin and hematoxylin) from Caesalpinia sappan were examined for their relaxant effects in isolated rat thoracic aorta. The methanolic extract significantly and dose-dependently relaxed the alpha (1)-receptor agonist phenylephrine-precontracted aortic rings, without affecting passive tension of these vessels. Removal of the vascular endothelium, inhibition of nitric oxide (NO) synthase with 0.1 mM N-omega-nitro-L-arginine and of cGMP biosynthesis with 10 muM methylene blue abolished the vasorelaxant effects of the herbal extract at doses up to 30 mug/ml. Similar vasorelaxant effects were observed with brazilin and hematoxylin. Therefore, these results suggest that brazilin and hematoxylin may be responsible for the vascular relaxant effects of C. sappan, via endogenous NO and subsequent cGMP formation. The vascular relaxant effects of the plant may contribute to its therapeutic actions. (C) 2000 Elsevier Science Inc. All rights reserved.